National and Global Petroleum Assessment Assessment of Undiscovered Gas Resources in the Lewis Shale Total Petroleum System of the San Juan Basin Province, New Mexico and Colorado, 2020

Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean resources of 2.6 trillion cubic feet of gas in the Lewis Shale Total Petroleum System of the San Juan Basin Province, New Mexico and Colorado.

Introduction encompasses marine rocks of the Lewis Shale from the deepest part of the central San Juan Basin to the maximum extent of the Lewis The U.S. Geological Survey (USGS) completed a geology- Shale to the northeast. The Lewis-Cliff House Continuous Gas AU based assessment of undiscovered, technically recoverable includes the extent of the Lewis Shale to the southwest in the San continuous, or unconventional, gas resources in the Lewis Shale of Juan Basin and additional production from the informally named the San Juan Basin in New Mexico and Colorado (fig. 1). The Lewis Shale was last assessed by the USGS in 2002 as part of a broad 109° 108° 107° 106° assessment of oil and gas resources within Jurassic and Cretaceous reservoirs in the San Juan Basin Province (Dubiel, 2013). Gas resources in the Lewis Shale Total Petroleum System (TPS) are 38° COLORADO primarily produced from shoreface sandstones of the Cliff House Sandstone and from recompletions of existing Mesaverde Group wells within marine clastic facies of the Lewis Shale. Gas production from recompleted wells in the Mesaverde Group is commingled with UTAH Lewis Shale production (Fassett and Boyce, 2005; Dubiel, 2013). Geologic Summary Marine strata of the Lewis Shale in the San Juan Basin 37° (Colorado and New Mexico) were deposited within the Cretaceous Western Interior Seaway. The Lewis Shale is composed of offshore marine shales, mudstones, siltstones, and sandstones, and interfingers with shoreface sandstones of the Cliff House Sandstone (informally known as the La Ventana and Chacra tongues) to the southwest of the central San Juan Basin. The Cliff House Sandstone tongues are units within the Mesaverde Group. The Lewis Shale has been informally divided into the Otero and Navajo City intervals below the Huerfanito 36° Bentonite Bed, a distinct volcanic ash marker bed within the Lewis Shale, and the Ute interval above the Huerfanito Bentonite Bed, which was deposited during the maximum marine transgression in the ARIZONA NEW MEXICO Campanian. The upper part of the Lewis Shale forms a gradational boundary with progradational shoreface sandstones of the overlying Pictured Cliffs Sandstone. The Lewis Shale has a maximum thickness of approximately 2,400 feet in the northeastern section of the basin (Fassett and Boyce, 2005; Dubiel, 2013). 35° The Lewis Shale is considered a self-sourced reservoir, where organic-rich marine rocks (containing Type II kerogen) were buried deep enough to reach the gas-generation window during the Base map from U.S. Department of the Interior, National Park Service 0 25 50 MILES Oligocene Period. Type III organic matter was also supplied to the WYOMING NEBRASKA 0 25 50 KILOMETERS basin from fluvial and deltaic systems to the southwest during Lewis UTAH COLORADO Shale deposition. Gas resources migrated locally from the Lewis PLANATIN NEVADA Lewis Shale Continuous Gas AU KANSAS Shale into clastic parasequences of the Cliff House Sandstones, Map forming the Lewis Shale TPS (Dubiel, 2013). Lewis-Cliff House Continuous Gas AU area ARIZONA Cliff House Fairway Continuous Gas AU NEW TEXAS MEXICO Assessment Units San Juan Province Basin boundary Three continuous assessment units (AUs) were defined for the Figure 1. Map showing the San Juan Basin Province, New Mexico Lewis Shale TPS: (1) Lewis Shale Continuous Gas AU, (2) Lewis- and Colorado, and the extents of the three continuous assessment Cliff House Continuous Gas AU, and (3) Cliff House Fairway units (AUs) in the Lewis Shale Total Petroleum System. Adjacent lines Continuous Gas AU (fig. 1). The Lewis Shale Continuous Gas AU indicate a shared boundary.

U.S. Department of the Interior Fact Sheet 2020–3048 U.S. Geological Survey November 2020 Table 1. Key input data for three continuous assessment units (AUs) in the Lewis Shale Total Petroleum System of the San Juan Basin Province, New Mexico and Colorado.

[Well drainage area, success ratio, and estimated ultimate recovery are defined partly using U.S. shale-gas analogs. The average estimated ultimate recovery input is the minimum, median, maximum, and calculated mean. Shading indicates not applicable. AU, assessment unit; %, percent; EUR, estimated ultimate recovery (per well); BCFG, billion cubic feet of gas] Lewis Shale Continuous Gas AU Lewis-Cliff House Continuous Gas AU Assessment input data— Calculated Calculated Continuous AUs Minimum Mode Maximum Minimum Mode Maximum mean mean Potential production area of AU (acres) 50,000 800,000 1,900,000 916,667 1,000 500,000 2,187,000 896,000 Average drainage area of wells (acres) 80 120 160 120 80 120 160 120 Area untested in AU (%) 96 97 99 97.3 98 99 100 99 Success ratio (%) 50 70 90 70 40 50 70 53.3 Average EUR (BCFG) 0.18 0.2 0.5 0.216 0.07 0.1 0.18 0.104 AU probability 1.0 1.0 Cliff House Fairway Continuous Gas AU Assessment input data— Calculated Continuous AUs Minimum Mode Maximum Lewis Shale Total Petroleum mean System Assessment Team Potential production area of AU (acres) 50,000 400,000 719,000 389,667 Kristen R. Marra, Christopher J. Average drainage area of wells (acres) 80 120 160 120 Schenk, Tracey J. Mercier, Heidi M. Area untested in AU (%) 70 80 90 80 Leathers-Miller, Marilyn E. Tennyson, Success ratio (%) 70 80 90 80 Thomas M. Finn, Cheryl A. Woodall, Average EUR (BCFG) 0.3 0.5 0.8 0.512 Michael E. Brownfield, Phuong A. Le, and AU probability 1.0 Ronald M. Drake II

Table 2. Results for three continuous assessment units (AUs) in the Lewis Shale Total Petroleum System of the San Juan Basin Province, New Mexico and Colorado.

[Results shown are fully risked estimates. F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. Shading indicates not applicable. BCFG, billion cubic feet of gas; NGL, natural gas liquids; MMBNGL, million barrels of natural gas liquids]

AU Accumu- Total undiscovered resources Total petroleum system and prob- lation Gas (BCFG) NGL (MMBNGL) assessment units (AUs) ability type F95 F50 F5 Mean F95 F50 F5 Mean Lewis Shale Total Petroleum System Lewis Shale Continuous Gas AU 1.0 Gas 361 1,066 2,112 1,133 1 2 5 2 Lewis-Cliff House Continuous Gas AU 1.0 Gas 102 374 853 414 0 0 1 0 Cliff House Fairway Continuous Gas AU 1.0 Gas 419 1,053 1,808 1,076 1 1 3 1 Total undiscovered continuous resources 882 2,493 4,773 2,623 2 3 9 3

Chacra and La Ventana sandstone trends to the south. The Cliff References Cited House Fairway Continuous Gas AU is defined to the northeast by the reservoir-pool line established by the New Mexico Oil Conservation Dubiel, R.F., 2013, Geology, sequence stratigraphy, and oil and gas Division for the Chacra sandstone producing interval. The southwest assessment of the Lewis Shale Total Petroleum System, San Juan boundary follows established production in shelf-sandstone beds of Basin, New Mexico and Colorado, chap. 5 of U.S. Geological Survey the informal Chacra sandstone trend. Key input data used to assess San Juan Basin Assessment Team, comps., Total petroleum systems and geologic assessment of undiscovered oil and gas resources in the the Lewis Shale TPS are listed in table 1. San Juan Basin Province, exclusive of Paleozoic rocks, New Mexico and Colorado: U.S. Geological Survey Digital Data Series 69–F, 45 p. Undiscovered Resources Summary Fassett, J.E., and Boyce, B.C., 2005, Fractured-sandstone gas reservoirs, The USGS assessed undiscovered, technically recoverable San Juan Basin, New Mexico and Colorado—Stratigraphic traps, continuous gas resources for three AUs in the Lewis Shale TPS not basin centered gas deposits—With an overview of Fruitland (table 2). Total estimated mean resources are 2,623 billion cubic Formation coal-bed methane, in Bishop, M.G., Cumella, S.P., feet of gas (BCFG), or 2.6 trillion cubic feet of gas, with an F95–F5 Robinson, J.W., and Silverman, M.R., eds., Gas in low-permeability range from 882 to 4,773 BCFG and 3 million barrels of natural gas reservoirs of the Rocky Mountain Region: Rocky Mountain liquids (MMBNGL) with an F95–F5 range from 2 to 9 MMBNGL. Association of Geologists, 2005 Guidebook CD–ROM, p. 109–185.

For More Information Assessment and methodology information can also be accessed at the USGS Energy Resources Program website at https://energy.usgs.gov.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/20203048